Obioban's 2005 IR/IR Coupe

[Obioban]

Shaikh talks a lot about preventing jacking down. Looking through these pictures, I found an interesting comparison, that makes it look like what he's doing in that regard.

The white M3 is on my former Ohlins' setup (I sold it to him). Same spring rates as me, same sway as me, same weight as me. Same corner, same grip level tires. My current setup has more bump and droop travel, so more space available for body roll. I believe the difference we're seeing is his setup has experienced jacking down, while mine has not.

It’s actually more exaggerated than the pics make it look, too, as the AW car is on 17 and I’m on 18s— so at static ride height, my wheels are closer to the fenders

[Tbonem3]

He can speed his rebound up a little.

[Obioban]

He can speed his rebound up a little.

He was 2 clicks off full soft. Any less and it never settles down.

[Tbonem3]

Then his springs are too light

[Obioban]

Then his springs are too light

25 lbs off stock Ohlins (and within Ohlins supported range of +-30%).

…. and bang on identical rates to me.

[Obioban]

Then his springs are too light

12 years ago, with 650lb front springs on my car.

[Tbonem3]

You're making a conclusion with confirmation bias due to having bought these really expensive dampers (which you tell others not to do), based off a photo.

You'd have to get a picture BEFORE the corner to see if his wheel is closer than yours aka being "packed up". Even then, it could be other factors. No, I don't believe your two cars' front driver corners, and in general, are the exact same.

Jacking down is a made up phrase from Shaikh. Foesn't exist. The phrase is pack up.

Him being deeper into the corner is less spring or heavier corner weight or he's faster . Maybe you have more compression dampening.

Packing up can lead to less control, harsher/harder ride. It's less comfortable as you're further into your travel as the bumps come. But it doesn't mean you dig deeper into a corner. Only speed (before loosing traction) can cause your wheel to compress more in a corner, given fixed spring rate and corner/car weight.

You're not even doing slaloms or something, it's just one corner as far as I can tell.

*Thought of another possiblity - you're talking a smoother line resulting in less compression.

[Obioban]

You're making a conclusion with confirmation bias due to having bought these really expensive dampers (which you tell others not to do), based off a photo.

You'd have to get a picture BEFORE the corner to see if his wheel is closer than yours aka being "packed up". Even then, it could be other factors. No, I don't believe your two cars' front driver corners, and in general, are the exact same.

Jacking down is a made up phrase from Shaikh. Foesn't exist. The phrase is pack up.

Him being deeper into the corner is less spring or heavier corner weight or he's faster . Maybe you have more compression dampening.

Packing up can lead to less control, harsher/harder ride. It's less comfortable as you're further into your travel as the bumps come. But it doesn't mean you dig deeper into a corner. Only speed (before loosing traction) can cause your wheel to compress more in a corner, given fixed spring rate and corner/car weight.

You're not even doing slaloms or something, it's just one corner as far as I can tell.

*Thought of another possiblity - you're talking a smoother line resulting in less compression.

"Jacking down" is not a phrase made up by Shaikh.
Here's Koni defining it: https://www.koni-na.com/en-US/NorthA...-Tuning-Guide/
Here's Eibach defining it: https://eibach.com/us/ft-3-eibach-su...-glossary.html

I plucked those two pictures because it was a nice side by side. But, the reason I noted this was was that, when I downloaded the pictures, my car is notably less rolled over in every picture than the photos from all previous events (on all previous setups) I've done for the last 15 years (despite my setup being softer than everything I've run other than the post flat ride converted Ohlins). It was the first thing that stuck out to me about the entire photo set-- the car was notably less rolled over than any previous event, in every cornering picture. I agree that two pictures in isolation would be meaningless-- I just meant them as an example of an overall trend.

Only speed (before loosing traction) can cause your wheel to compress more in a corner, given fixed spring rate and corner/car weight.

Speed is not the only cause of suspension compression mid corner-- bumps still exist in corners, and compress the suspension. If there's too much rebound, the cornering load does not allow the suspension to return to the static loaded ride height. Next bump repeats the process. This can continue until you're in the bump stops, increasing the effective spring rates. decreasing girp. This is what jacking down is.

Or, as Koni put it in the link above,

Too much rebound control in relation to spring rate will cause a condition known as "jacking down." This is a condition where, after hitting a bump and compressing the spring, the damper does not allow the spring to return to a neutral position before the next bump is encountered. This repeats with each subsequent bump until the car is actually lowered onto the bump stops. Contact with the bump stops causes a drastic increase in roll stiffness. If this condition occurs on the front, the car will understeer; if it occurs on the rear, the car will oversteer.

[K-Dawg]

The car looks great!

I don't think you've commented much on how the FCM dampers behave around town, as far as comfort and civility go.

Agreed that flat ride is huge. Now, when people say that their non-flat ride suspension rides/handles nicely, I tend to stop listening.

As for the AC, you might try just getting a proper vacuum and refill on the system and doing what you can to clean the condenser. Although at that point, changing the condenser is probably not much more work.

[Obioban]

The car looks great!

I don't think you've commented much on how the FCM dampers behave around town, as far as comfort and civility go.

Agreed that flat ride is huge. Now, when people say that their non-flat ride suspension rides/handles nicely, I tend to stop listening.

As for the AC, you might try just getting a proper vacuum and refill on the system and doing what you can to clean the condenser. Although at that point, changing the condenser is probably not much more work.

$87 for an OEM (Mahle) condenser, so I feel like it's probably worth swapping it if I'm going through the effort of cleaning it and already draining/filling it. With 160,000 miles on it (bending the fins, gumming up), it's probably hurting the rads performance, too.

That said, short term I'm going to do nothing. While we're building our house, I don't have any good place to do car work-- so projects are limited to either being superficial (trackconnect module) or necessary... or... pay someone to do it 😲. Trying to avoid the last.

On nicely paved to fine backroads, the FCMs are magic. As in, I didn't know it was possible for a car to be this good.

On large potholes, they are not as good as the flat ride converted Ohlins were.

In terms of ride quality, they're firm but not harsh. Ride quality is pretty similar to my Dinan springs (which are flat ride)/Koni M3 (wagon). Small/medium bump ride quality is better than the Ohlins were, large bump/potholes are worse than the Ohlins were. At highway speeds (+), they're always pretty great.

[IamFODI]

Maybe you have more compression dampening.

One FCM signature is less "rebound bias", a.k.a. a much higher ratio of compression damping to rebound damping (vs. other dampers). At the same time, Shaikh has said he likes to run minimum necessary damping, so a higher compression:rebound damping ratio doesn't necessarily mean more absolute compression damping.

Either way, I agree that this isn't slam-dunk proof of less "jacking down", though it's certainly consistent with that hypothesis.

[Obioban]

I can confirm when I get home, but I believe my compression and rebound damping are roughly 1:1.

[Tbonem3]

Why would the white car be lower in its stroke before that corner? Tarmac doesn't look undulated. Are you saying the bumps were large enough to cause visible packing, but small enough they can't be seen on the tarmac in the photos?

I'm writing this because you've told all and sundry, for years, that this type of stuff was all in their head. But you get to post 2 pics (where you can barely even tell any difference [between 2 different cars, no less]), and come to conclusions?

Very anti-science of you.

[K-Dawg]

[Obioban]

Why would the white car be lower in its stroke before that corner?

I'm not sure what you're asking here.

Tarmac doesn't look undulated. Are you saying the bumps were large enough to cause visible packing, but small enough they can't be seen on the tarmac in the photos?

Yes.

The size of the bump doesn’t matter— the question is if the spring is strong enough to overpower the cornering load + shock rebound + bump input. The world is full of tiny bumps.

I'm writing this because you've told all and sundry, for years, that this type of stuff was all in their head. But you get to post 2 pics (where you can barely even tell any difference [between 2 different cars, no less]), and come to conclusions?

Very anti-science of you.

I see where you're coming from, with the two photo thing. I just meant them as an example-- specifically because the white car is running the exact setup my car was on last year (as in, the parts I took off my car), as well as most of the other mods I have done, on the same corner, at a similar pace. It's about as good of a comparison as you could hope for.

That said, my real observation was when I opened the photo album-- it was immediately apparent to me that my car was notably less rolled over in every photo compared to every previous setup I've run. I posted the 2 picture comparison to the white car because it was an easy visualization of it, not as proof of anything.